The invention concerns a wire shaped product with high wear resistance which product is cold drawn and subsequently flattened through cold-rolling, hardened and tempered, consisting of a martensitic stainless chromium steel. The invention also concerns a method relating to the manufacturing of such wire-shaped product, which can be employed for the manufacturing of wear parts in combustion engines, particularly compression rings and oil scraper rings for cylinder pistons. The invention also includes such wear parts, particularly compression rings.
The most common material for compression rings in combustion engines is cast iron. A typical composition of such a cast iron contains 3.50-3.95% C, 2.20-3.10% Si and 0.40-0.80% Mn. Also compression rings of steel, including stainless martensitic chromium steels, are used to a considerable extent. A steel of that type which is employed for compression rings has the composition 0.70% C, 0.40% Si, 0.35% Mn, 14.0% Cr and 0.30% Mo, balance iron and impurities. A requirement which is raised on compression rings, particularly on the so called top ring, which is journalled in, a circumferential groove adjacent to the piston top, is that it shall have a high wear resistance which is maintained even after a long time of exposure to high tempers and corrosive media. In order to satisfy these requirements, also a stainless martensitic steel which consists of 0.90% C, 0.40 Si, 0.40 Mn, 18.0 Cr, 0.9 V, 1.0 Mo, balance iron and impurities, is used to a considerable extent. The wire-shaped product which has been cold drawn and cold-rolled to its final cross section, e.g. 1xc3x973 mm, bright hardened and tempered by the material supplier, is spun by the compression ring manufacture to helical, so called xe2x80x9cslinkiesxe2x80x9d in a slinky-machine. There is a problem that wires made of this high chromium, martensitic chromium steel easily rupture in connection with the spinning operation because of an insufficient ductility of the material. An other problem is that this wire-shaped product is expensive, which only to a small degree depends on the price of the alloy elements but basically on a very cumbersome manufacturing of the cold drawn and cold-rolled wire and, not least, on much rejected material because of failures during the manufacturing.
It is a purpose of the invention to address this complex of problems. More particularly, the invention aims at providing a wire-shaped product of the kind mentioned in the preamble, which has a good ductility and which therefore is suited to be spun in slinky-machines with a smaller risk for ruptures than what has previously been possible, and to be able to reproducibly manufacture from such a spun product, compression rings which have a high and even wear resistance and a good corrosion resistance.
It is also a purpose of the invention to simplify, and consequently to reduce the costs for the entire process in connection with the cold drawing of the wire, through a reduction of the number of steps in the process.
The improvements on which the invention is based can also be employed for the development of wire-shaped products of martensitic stainless steels, which have higher contents of included alloy elements than what previously has been possible with a good production economy within this technical field. Besides the above mentioned, martensitic chromium steels, thus a variety of steels having different chemical compositions are conceivable within the frame of the invention. Conceivable are for example steels which contain in weight-%: 1-2 C, 0-1.5 Si, 0-1 Mn, max 0.050 P, max 0.050 S, 22-27 Cr, 0.5-1.5 Mo, 0.5-1.0 V, balance essentially only iron and impurities. Within the said range, e.g. a steel can be conceived which has the nominal composition 1.2 C, 0.9 Si, 0.5 M, max 0.050 P, max 0.050 S, 22 Cr, 0.5 Mo, 0.5 V, balance essentially only iron and impurities. Another conceivable, nominal composition may be 1.7 C, 1.1 Si, 0.8 Mn, max 0.050 P, max 0.050 S, 27 Cr, 1.0 Mo, 0.7 V, balance essentially only iron and unavoidable impurities.
The above and other objectives of the invention can be achieved therein that the invention is characterized by what is stated in the accompanying patent claims. Further features and aspects of the invention will be apparent from the following, detailed description of the invention and from described examples and performed experiments.